1. Field
The present invention relates to a light emitting diode and a method of fabricating the same, and more particularly, to a light emitting diode including a plurality of light emitting cells connected to each other via interconnections on a single substrate, and a method of fabricating the same.
2. Discussion of the Background
Gallium nitride (GaN) based light emitting diodes (LEDs) have been used in a wide range of applications including full color LED displays, LED traffic sign boards, white LEDs, etc. In recent years, with higher luminous efficacy than existing fluorescent lamps, white light emitting diodes are expected to overtake existing fluorescent lamps in the field of general lighting.
A light emitting diode may be driven to emit light by forward current and require a supply of direct current. Thus, when the light emitting diode is directly connected to an alternating current (AC) source, the light emitting diode repeats on/off operation dependent upon a direction of electric current, and cannot continuously emit light and may be easily damaged by reverse current.
To solve such problems of a light emitting diode, WO 2004/023568 (A1) of Sakai et. al., entitled “LIGHT-EMITTING DEVICE HAVING LIGHT-EMITTING ELEMENTS”, discloses a light emitting diode which can be used through direct connection to a high voltage AC source.
The AC light emitting diode of WO 2004/023568 (A1) includes a plurality of light emitting elements connected to each other via an air bridge interconnection to be driven by an AC source. Such an air-bridge interconnection may be easily broken by external force and may cause short circuit due to deformation by external force.
To solve such a drawback of the air bridge interconnection, AC light emitting diodes are disclosed in Korean Patent Nos. 10-0690323 and 10-1186684, for example.
FIG. 1 is a schematic plan view of a typical light emitting diode including a plurality of light emitting cells, and FIG. 2 and FIG. 3 are sectional views taken along line A-A of FIG. 1.
Referring to FIG. 1 and FIG. 2, the light emitting diode includes a substrate 21, a plurality of light emitting cells 26 including S1, S2, a transparent electrode layer 31, an insulation layer 33, and an interconnection 35. In addition, each of the light emitting cells 26 includes a lower semiconductor layer 25, an active layer 27, and an upper semiconductor layer 29, and a buffer layer 23 may be interposed between the substrate 21 and the light emitting cells 26.
The light emitting cells 26 are formed by patterning the lower semiconductor layer 25, active layer 27, and upper semiconductor layer 29 grown on the substrate 21, and the transparent electrode layer 31 is formed on each of the light emitting cells S1, S2. In each of the light emitting cells 26, an upper surface of the lower semiconductor layer 25 is partially exposed by partially removing the active layer 27 and the upper semiconductor layer 29 for connection to the interconnection 35.
Next, the insulation layer 33 is formed to cover the light emitting cells 26. The insulation layer 33 includes a side insulation layer 33a covering side surfaces of the light emitting cells 26 and an insulation protective layer 33b covering the transparent electrode layer 31. The insulation layer 33 is formed with an opening through which a portion of the transparent electrode layer 31 is exposed and an opening through which the lower semiconductor layer 25 is exposed. Then, the interconnection 35 is formed on the insulation layer 33, in which a first connection section 35p of the interconnection 35 is connected to the transparent electrode layer 31 of one light emitting cell S1 through the opening of the insulation layer 33, and a second connection section 35n of the interconnection 35 is connected to the lower semiconductor layer 25 of another light emitting cell S2 adjacent the one light emitting cell S1 through the other opening of the insulation layer 33. The second connection section 35n is connected to an upper surface of the lower semiconductor layer 25, which is exposed by partially removing the active layer 27 and the upper semiconductor layer 29.
In a conventional technique, the interconnection 35 is formed on the insulation layer 33 and thus may be prevented from deformation by external force. In addition, since the interconnection 35 is separated from the light emitting cells 26 by the side insulation layer 33a, it is possible to prevent short circuit of the light emitting cells 26 by the interconnection 35.
However, such a conventional light emitting diode may have a limit in current spreading in areas of the light emitting cells 26. Specifically, electric current may be concentrated under one end of the interconnection 35 connected to the transparent electrode layer 31 instead of being evenly spread in the areas of the light emitting cells 26. Current crowding may become severe with increasing current density.
Moreover, such a conventional light emitting diode may have problems in that some of the light generated in the active layer 27 may be absorbed and lost by the interconnection 35, and the thickness of the insulation layer 33 may need to be increased to prevent formation of defects such as pin-holes and the like.
Furthermore, since a portion of the upper surface of the lower semiconductor layer 25 is exposed for electric connection of the second connection section 35n, the active layer 27 and the upper semiconductor layer 29 are partially removed, and may thereby reduce an effective light emitting area.
In order to prevent current crowding, a current blocking layer 30 may be disposed between the transparent electrode layer 31 and the light emitting cells 26 to prevent current crowding under the connection end of the interconnection 35.
FIG. 3 is a sectional view of a light emitting diode including a current blocking layer 30 in the related art.
Referring to FIG. 1 and FIG. 3, the current blocking layer 30 is disposed under the connection end of the interconnection 35, and may thereby prevent current crowding under the connection end of the interconnection 35. In addition, the current blocking layer 30 may be formed as a reflector such as a distributed Bragg reflector, and may thereby prevent light generated in the active layer 27 from being absorbed into the connection end of the interconnection 35.
However, when the current blocking layer 30 is additionally formed as shown in FIG. 3, a photolithography process for forming the current blocking layer 30 is added, and may thereby increase manufacturing costs.
Moreover, as in the light emitting diode of FIG. 2, the light emitting diode of FIG. 3 may also have problems, such as optical loss due to absorption of light generated in the active layer 27 by the interconnection 35, reduction in effective light emitting area, and increase in thickness of the insulation layer 33 to prevent defects such as pinholes in the insulation layer 33.